Function securing unit for communication systems

ABSTRACT

A communication system having at least one first and a second communication unit. The first communication unit has a counter memory unit which stores a counter value, and is designed such that the occurrence of a first communication event prompts the counter value in the counter memory unit to be changed in a defined first manner. At least the occurrence of a defined reference event is followed by the counter value in the counter memory unit being changed in a defined second manner. In the course of a second defined communication event, the first communication unit transmits the current counter value in the counter memory unit to the second communication unit.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Phase Application of PCTInternational Application No. PCT/EP2010/051322, filed Feb. 3, 2010,which claims priority to German Patent Application No. 10 2009 007200.4, filed Feb. 3, 2009, the contents of such applications beingincorporated by reference herein.

FIELD OF THE INVENTION

The invention relates to a communication system to a method forsynchronization and to the use of the communication system in motorvehicles.

BACKGROUND OF THE INVENTION

The inventors sought to develop a communication system and the methodfor synchronization which allows synchronous communication between atleast two communication units in a relatively inexpensive manner and/orwhich allows a relatively high level of system security forcommunication between communication units in the system.

SUMMARY OF THE INVENTION

This is achieved by means of a communication system having at least onefirst and a second communication unit, wherein the first communicationunit has a counter memory unit which stores a counter value (MSG_CNT),wherein the first communication unit is designed such that at least theoccurrence of a first defined communication event prompts the countervalue in the counter memory unit to be changed in at least one definedfirst manner, wherein at least the occurrence of a defined referenceevent is followed by the counter value in the counter memory unit beingchanged in at least one defined second manner, wherein at least in thecourse of a second defined communication event the first communicationunit transmits the current counter value in the counter memory unitdirectly or indirectly to the second communication unit. The inventionalso achieves this by means of a method for synchronizing thecommunication between at least one first and a second communication unitin a communication system wherein the first communication unit has acounter memory unit which stores a counter value (MSG_CNT), wherein theoccurrence of a first defined communication event prompts the countervalue in the counter memory unit to be changed in at least one definedfirst manner, and wherein the occurrence of a defined reference eventprompts the counter value in the counter memory unit to be changed in atleast one defined second manner, wherein at least in the course of asecond defined communication event the first communication unittransmits at least the current counter value (MSG_CNT) in the countermemory unit directly or indirectly to the second communication unit.

The communication system and the method are designed particularly toincrease dependability in an electronic system.

The term dependable is preferably understood to mean the term “failsafe” and/or “fail silent”.

The description for the occurrence is preferably understood to meanafter the occurrence.

The first and second communication events are preferably defined as acommunication event which occurs or can occur at least in thecommunication between the first and second communication units.

The counter memory unit is preferably designed such, and/or ispreferably actuated such, that the change in the counter value in thedefined first manner is effected by a defined step size using amathematical operation. The mathematical operation is understood to meanparticularly addition or multiplication or a more complex operation, andthe step size is understood to mean, by way of example, the value bywhich the counter value is incremented or decremented, with particularpreference by the value one, or the value which is multiplied by thecounter value.

The counter memory unit is preferably designed such, and/or is actuatedsuch, that every communication event between communication units in thecommunication system, such as the first and second communication units,prompts the counter value in the counter memory unit to be changed inthe defined first manner. With particular preference, the firstcommunication event is defined such that every communication eventbetween communication units in the communication system is handled atleast as the defined first communication event.

It is preferred that the counter memory unit is designed and/or actuatedas a counter unit, wherein the change in the counter value in thedefined second manner is in the form of a set operation or resetoperation for the counter unit. This set or reset operation prompts thecounter value to be reset particularly to a defined value, withparticular preference the value “0”.

The first communication unit preferably has at least one first and asecond data memory unit and is designed such that at least theoccurrence of the first defined communication event prompts the currentdata item in the first data memory unit to be written to the second datamemory unit and prompts the counter value in the counter memory unit tobe changed in the defined first manner. By way of example, this is basedon the form for a special mode of operation called a continuous mode ofoperation or “continuous mode”, in which the counter value in thecounter memory unit is with particular preference not reset.

As an alternative preference, the first communication unit has at leastone first and a second data memory unit and is designed such that theoccurrence of a defined trigger event, particularly a defined thirdcommunication event or an internal trigger event, is followed by thecurrent data item in the first data memory unit being written to thesecond data memory unit and, with particular preference thereafter, thecounter value in the counter memory unit being changed in the definedsecond manner. With quite particular preference, the writing of thecurrent data item in the first data memory unit to the second datamemory unit is followed by the then stored data in the first and seconddata memory units being compared in a transfer unit. The comparisonresult from this comparison is used further as status information.

It is preferred that the first communication unit is designed such thatin the course of at least the second defined communication event betweenat least the first and second communication units the current data itemin the second data memory unit is transmitted from the firstcommunication unit to the second communication unit.

It is expedient that the second communication unit is designed as amaster unit and at least the first communication unit is designed as aslave unit, and these units are connected to one another by a bussystem.

The first communication unit is preferably designed as a sensor unitand/or actuator unit which, in particular, captures at least onemeasured variable and provides at least one measured variable data item.

The second communication unit is preferably designed as an electroniccontrol unit, particularly as an electronic control unit in a motorvehicle braking system and/or in a motor vehicle electronic stabilitycontrol system.

It is preferred that the counter memory unit is designed and actuatedsuch that the counter value is designed to be able to be used as a timestamp and/or that the counter value forms or provides a time measure forsynchronizing the communication system.

The reference event is preferably defined as the, in particularsuccessful, operation of writing the data item in the first data memoryunit to the second data memory unit.

The third defined communication event is preferably defined as a dataquery or “sample command” from the second communication unit at least tothe first communication unit, particularly to all further communicationunits in the communication system.

The internal trigger event is preferably defined as the transgressionabove or below a measured value or parameter in the first communicationunit.

The second defined communication event expediently comprises data accessby the second communication unit at least to the first communicationunit, which involves the current counter value and the data itemcurrently stored in the second data memory unit being transmitted orsent, in particular together, from the first communication unit to thesecond communication unit.

It is preferred that the first communication unit is designed as asensor and/or actuator unit and has at least one first statusinformation processing module which comprises a status memory unit whichstores a status information item for this first communication unit inthe form of a status data item, wherein the first status informationprocessing module furthermore comprises a masking memory unit, connectedto the status memory unit, and also a status processing element which isconnected to this masking memory unit, wherein the first statusinformation processing module is designed such that at least one statusinformation item from the status data item is selected by the maskingmemory unit and the resulting selective status data item is processed bythe status processing element such that the output of said maskingmemory unit provides a short status data item, which has a shorter dataword length than the selective status data item.

The masking memory unit preferably comprises a logic circuit or aselection circuit which is used to link the status data item at theinput to the bit mask stored in the masking memory unit, as a result ofwhich the selective status data item is produced. This logic circuit orselection circuit particularly comprises an AND logic circuit which,with particular preference, is designed such that each bit of the statusdata item is ANDed with a respective bit from the bit mask.

Preferably, the first status information processing module additionallyhas a short status memory unit which is connected to the statusprocessing element and to which the short status data item is written.

The first communication unit preferably comprises an interface unitwhich is connected to the output of the status processing element or tothe output of the short status memory unit in the first statusinformation processing module and is connected to the masking memoryunit in the first status information processing module such that it canchange and/or overwrite the bit mask stored in the masking memory unit,as a result of which it is possible to customize the selection of thestatus types which are used to provide the interface unit withinformation in the form of the short status data.

Alternatively, the short status memory unit is preferably integrated inthe interface unit.

It is preferred that the interface unit is furthermore connected to thestatus memory unit in at least the first status information processingmodule in such a way, and is designed in such a way, that it can writeto this status memory unit, as a result of which it is possible for atest status data item to be written to the status memory unit. For thispurpose, the interface unit particularly has a test unit which isdesigned such that it automatically provides test data or forwardsand/or processes test data, with particular preference test data whichare provided by a second communication unit.

Expediently or alternatively, the communication unit preferably has atleast one signal processing unit which produces and/or providesparticularly a test module in addition or as an alternative to the testunit in the interface module.

Preferably, the first communication unit additionally has at least onesecond, redundant status information processing module which isessentially designed on the basis of the first status processing moduleand is likewise connected to the interface unit essentially in the sameway.

The first communication unit is preferably part of a communicationsystem and connected to at least one second communication unit, whereinthe interface unit of the first communication unit is designed such thatit can transmit the short status data item from the first and/or thesecond status information processing module and/or a total short statusdata item, which is derived from one or both of these data items, to thesecond communication unit. The interface unit of the first communicationunit is particularly designed such that it writes a test status dataitem which has been received from the second communication unit to thestatus memory unit in the first and/or status information processingmodule directly or in modified form and then transmits at least one ofthe short status data items resulting therefrom and/or a total shortstatus data item derived therefrom to the second communication unit.

The expression “the communication unit” itself, that is to say withoutnumbering, expediently always means the first communication unit, whichis designed as a sensor and/or actuator unit.

The status memory units in the first and second status informationprocessing modules are expediently connected such, and/or are actuatedsuch, that the respective status data in these two status memory unitsare, at least in relation to status information which is provided by thecommunication unit itself, in the form of data words which are theinverse of one another. In particular, the masking memory units in thefirst and second status information processing modules are connectedsuch, and/or are actuated such, that the respective bit masks in thesetwo masking memory units are in the form of data words which are theinverse of one another.

The method according to the invention is preferably developed by virtueof the first communication unit having at least one first and a seconddata memory unit, wherein the occurrence of a defined trigger event,particularly a defined third communication event or an internal triggerevent, is followed by the current data item in the first data memoryunit being written to the second data memory unit and by the countervalue in the counter memory unit being changed in the defined secondmanner, and wherein the occurrence of the defined second communicationevent is followed by the current data item in the second data memoryunit being transmitted or sent at least from the first communicationunit to the second communication unit.

Furthermore, the method is expediently developed further by virtue ofthe transmission of status information from the first communicationunit, which is designed as a sensor and/or actuator unit, to at leastthe second communication unit involving the first communication unithaving at least one first status information processing module with astatus memory unit which stores status information from said firstcommunication unit in the form of a status data item, wherein at leastone status information item from this status data item from the firststatus information processing module is selected by means of a maskingmemory unit, after which the resulting selective status data item isprocessed by a status processing element and this status processingelement provides a short status data item, which has a shorter data wordlength than the selective status data item.

The method for transmitting status information is preferably developedfurther by virtue of the at least one short status data item beingtransmitted via an interface unit to the second communication unit.Accordingly, it is particularly preferred that the second communicationunit interprets the short status data item regarding whether the shortstatus data item contains an information item indicating that the secondcommunication unit is intended to react thereto, after which, if thepresence of such an information item to which the second communicationunit is intended to react is identified, the second communication unitrequests or reads at least the status data item from the first and/orthe second status information processing module and/or the secondcommunication unit automatically puts itself into another mode ofoperation, particularly into an emergency mode of operation. With quiteparticular preference, the second communication unit is designed suchthat it stores information relating to the interpretation of the atleast one short status data item and/or the total short status dataitem.

The invention also relates to the use of the communication system inmotor vehicles, particularly in a motor vehicle braking system and/or ina motor vehicle electronic stability control system.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed descriptionwhen read in connection with the accompanying drawings. Included in thedrawings is the following figures:

FIG. 1 shows an exemplary embodiment of a communication system with afirst and a second communication unit, wherein the first communicationunit is designed as a sensor unit and comprises a counter memory unit,and

FIG. 2 shows the exemplary form of a first and a second statusinformation processing module and the connection thereof to an interfaceunit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an exemplary dependable communication system, comprising afirst communication unit 1, for example designed as a pressure sensorunit, which is connected by means of a data transmission link 3 to asecond communication unit 2, which is designed as an electronic controlunit ECU. In this case, the sensor unit 1 has two pickups SE1, SE2, forexample two pressure sensor elements. These are connected to ananalog/digital converter ADC which, by way of example, provides twodigital pressure values P1, P2 and two digital temperature values T1, T2per measurement. This analog/digital converter ADC is connected by meansof a multiplexer Mux to a signal processing unit 4, for example designedas a digital signal processor DSP. In addition, the multiplexer Mux isalso used to supply at least one further signal line, for example testsignal lines TEST to the signal processing unit 4. For the principalinformation or pressure information P1, P2 which the sensor unit 1 isintended to deliver to the control unit 2, the sensor unit 1 has a firstand a second serial data memory unit MemA and MemB for the purpose ofsynchronization. In this case, for each measurement/evaluation operationor cycle, the principal information, for example two digital pressurevalues P1, P2 and two digital temperature values T1, T2, is written tothe first data memory unit MemA, which is used as buffer store. Thisalways involves the first data memory unit MemA being overwritten. Inline with the example, the signal processing unit 4 automatically writesto the first data memory unit MemA when there are new data available.

The sensor unit 1 has a counter memory unit 7 which stores a countervalue (message counter) MSG_CNT which corresponds to a time stamp ortime measure for synchronous communication within the communicationsystem. At least a first communication event, in line with the exampleevery communication event between the first and second communicationunits, prompts the counter value to be changed in a defined firstmanner. In line with the example, this is done by means of actuation bythe interface unit “logic”, 6. The counter memory unit 7 is designed asa counter unit, and the actuation in the first manner is defined—in linewith the example—as incrementation of the counter value by 1.

A data query or a “sample command” from the second communication unit 2,ECU, which, in line with the example, is defined as a thirdcommunication event, is interpreted by the sensor unit 1 as a triggerevent, on the basis of which the sensor unit 1 transmits or writes thecurrent data item in the first data memory unit MemA to the second datamemory unit MemB. Such a successful write operation from MemA to MemBafter the trigger event is defined as a reference event, the occurrenceof which is followed by the counter value in the counter memory unit 7or counter unit being changed in a defined second manner, which in linewith the example corresponds to the counter value being reset to thevalue “0”. As a result, the query operation by the second communicationunit ECU is linked to the reset of the counter value for the purpose ofsynchronization. There then follows data access or a read command by thesecond communication unit, for example, which access or command isdefined as a second communication event. The data item stored in thesecond data memory unit MemB and the current counter value are thentransmitted from the sensor unit 1 to the control unit ECU, 2. Thistransmission is effected by the interface unit ‘logic’, 6, and—in linewith the example—the driver unit 5 connected downstream thereof.

The control unit 2 thus triggers the data transmission with the thirdcommunication event in order to select the current data at the exactrequest time in each case—the current data item in the first data memoryMemA is written to the second data memory MemB. This data item from MemBis then made available to the driver unit 5 together with the currentcounter value via the interface unit 6, ‘logic’, after data access bythe ECU, which is defined as a second communication event, and saiddriver unit transmits these data via the data transmission link 3 to thecontrol unit 2.

The signal processing unit 4 furthermore provides status informationstat which is supplied to a first and a redundant second statusinformation processing module 8 and 9, which are connected to theinterface unit ‘logic’, 6. These two status information processingmodules 8, 9 allow efficient and resource-saving transmission of statusinformation from the sensor unit 1 to the control unit 2.

The sensor unit 1 additionally has a central memory unit Mem1 which—inline with the example—is designed as an EEPROM unit and which storesdefined operating parameters for the sensor unit. This central memoryunit Mem1 is likewise connected to the signal processing unit 4 and tothe interface unit logic.

In line with the example, the memory units MemA and MemB each comprise aregister for each principal information data item P1, P2, T1 and T2.

The central memory unit Mem1 optionally comprises a hardwareidentification information item ID which the control unit ECU can queryand which can be used to explicitly identify the sensor unit 1. Thismakes it possible to avoid the use of a sensor unit—not provided—ininteraction with a particular control unit, for example.

In order to further increase dependability, provision is optionally madefor the control unit ECU to compare the pressure values P1 and P2captured by the pressure sensor elements SE1 and SE2 and provided by thesignal processing unit 4 for the purpose of plausibility checking. Theanalog/digital converter ADC and/or the signal processing unit 4 cannotbe ruled out from influencing the pressure signals in a similar,undesirable manner. Therefore, the pressure values P1 and P2 are—in linewith the example—represented or encoded in different manners, forexample as data with inverse coding relative to one another or by arelative offset which is known to the control unit 2.

Furthermore, at defined times, for example in a test mode of the sensorunit 1, one or more test data items are provided on test signal linesTest and allow the control unit 2 to check whether, by way of example,filter parameters or other signal processing functions of the signalprocessing unit 4 are working correctly. In line with the example, thecontrol unit 2 prescribes these test values at runtime in each case orinitializes a BIST (built-in in self test)—implemented completely in thesensor unit 1—with appropriately stored test vectors or test data, theseor the output data associated therewith being known to the control unit2.

So as to be optionally able to additionally recognize an erroneousselect line or the function thereof in the multiplexer Mux, the pressurevalues P1 and P2 are checked for plausibility in the control unit 2,particularly directly following the processing of test data, for exampleusing a pressure model or using particular threshold values/differentialvalue thresholds.

This plausibility check on at least the pressure values P1 and P2 can beperformed by way of example on a “braking system level” when thecommunication system described here is part of a motor vehicle brakingsystem and the sensor unit 1 captures braking pressure values and thecontrol unit 2 is designed as the electronic control unit of the brakingsystem.

The time base of the time stamp or the respective current counter valueis known both to the sensor unit 1 and to the control unit ECU. Thistime stamp allows possible sample/timing and/or synchronization errorsto be recognized, in particular for the data transmission via the datatransmission link 3.

By way of example, the data transmission link 3 merely comprises asingle data transmission line.

The data memory units MemA, MemB optionally have an associated transferunit ‘transfer’ for example, which comprises a logic circuit which isused to compare the data in the memory MemA directly before thetransmission of the data in the buffer store MemA to the memory MemBwith the data in the memory MemB directly after this very transmission.The result is written to a status register ‘transfer Status’.Furthermore, the transfer unit ‘transfer’ has a test logic circuit whichis used to test the logic circuit. In line with the example, thetransmission of the data from MemA to MemB and/or the transfer unitis/are additionally checked by the transmission of test data from MemAto MemB.

FIG. 2 is used to illustrate the design and actuation of the redundantstatus information processing modules 8 and 9 of the sensor unit. Theserespectively comprise a status memory unit 10, a masking memory unit 11,a status processing element 12 and, in line with the example, a shortstatus memory unit 13, which is/are alternatively each or jointlyintegrated in the interface unit 6, ‘logic’, for example. The statusmemory unit 10 is supplied with a respective status data item stat, inline with the example by the signal processing unit 4, which is notshown here, and said status data item is stored in the status memoryunits 10. These make the respective status data item stat available tothe masking memory unit 11, which stores a bit mask and in which thestatus data item stat is ANDed with the respective bit mask, as a resultof which the bit mask selects defined status bits or status information.For this purpose, the masking memory unit 11 has a respective logiccircuit—not shown—or selection circuit. This logic circuit or selectioncircuit comprises particularly an AND logic circuit which, in line withthe example, is designed such that each bit of the status data item isANDed with a respective bit of the bit of the bit mask.

The resulting selective status data item sel-stat is processed in thestatus processing element 12, so that a short status data item k-stat isprovided, which has a shorter data word length than the selective statusdata item sel-stat. In line with the example, the status processingelement 12 is designed such that it ORs the individual bits of theselective status data item sel-stat. The short status data item k-statis stored in the short status memory unit 13 and made available to theinterface unit 6. In line with the example, the exemplary ORing of theindividual bits of the selective status data item means that the shortstatus data item k-stat comprises only one bit, which contains a pieceof information regarding whether one or more, that is to say whether atleast one, of the status bits which are selected by the masking memoryunit has/have the value “1”. The short status data item k-stat in eachstatus information processing module 8, 9 or a common total short statusdata item is sent to the second communication unit—which is not shownhere. If the latter identifies the occurrence of an error or of anundesirable status, the interface unit 6 reads one or both of the statusmemory units and sends the respective complete status data item to thesecond communication unit. The interface unit 6 is designed andconnected to the masking memory unit 12 such that read and write accessare possible. The write access or the changing or writing of the bitmask allows the selection of the individual status bits of the statusdata item to be prescribed.

By way of example, the interface unit 6 has a test unit—not shown—whichis designed such that it automatically provides test data or forwardsand/or processes test data, with particular preference test data whichare provided by a second communication unit. These test data arerespectively written to the status memory unit of the status informationprocessing modules 8, 9 by the interface unit, and the result isassessed with respect to the result that is to be expected. It is thuspossible to test the workings of the status information processingmodules 8, 9.

As an alternative example, the status information processing modules 8,9 do not have any short status memory units, but rather the respectiveshort status data item k-stat is made available to the interface unit,which is designed such that it ORs these two short status data itemsk-stat and produces a total short status data item which is derivedtherefrom in this manner and which is transmitted to the secondcommunication unit, for example.

The invention claimed is:
 1. A communication system having at least afirst and a second communication unit, wherein the first communicationunit has a counter memory unit which stores a counter value (MSG_CNT),wherein the first communication unit is configured such that at least anoccurrence of a first defined communication event prompts the countervalue in the counter memory unit to be changed in at least one definedfirst manner, wherein at least an occurrence of a defined referenceevent is followed by the counter value in the counter memory unit ischanged in at least one defined second manner, wherein at least in thecourse of a second defined communication event the first communicationunit transmits the current counter value in the counter memory unitdirectly or indirectly to the second communication unit, wherein thefirst communication unit has at least one first and a second data memoryunit (MemA, MemB) and is configured such that at least the occurrence ofthe first defined communication event prompts a current data item in thefirst data memory unit (MemA) to be written to the second data memoryunit (MemB) and prompts the counter value (MSG_CNT) in the countermemory unit to be changed in the defined first manner.
 2. Thecommunication system as claimed in claim 1, wherein the counter memoryunit is configured and/or actuated such that the change in the countervalue (MSG_CNT) in the defined first manner is effected by a definedstep size using a mathematical operation.
 3. The communication system asclaimed in claim 1, wherein the counter memory unit is configured and/oractuated such that every communication event between the first andsecond communication units in the communication system prompts thecounter value (MSG_CNT) in the counter memory unit to be changed in thedefined first manner.
 4. The communication system as claimed in claim 1,wherein the counter memory unit is configured and/or actuated as acounter unit, wherein the change in the counter value in the definedsecond manner is in the form of an operation for setting the counterunit to a defined counter value.
 5. The use of the communication systemas claimed in claim 1 in motor vehicles.
 6. The use of the communicationsystem as claimed in claim 5 in a motor vehicle braking system and/or ina motor vehicle electronic stability control system.
 7. A communicationsystem having at least a first and a second communication unit, whereinthe first communication unit has a counter memory unit which stores acounter value (MSG_CNT), wherein the first communication unit isconfigured such that at least an occurrence of a first definedcommunication event prompts the counter value in the counter memory unitto be changed in at least one defined first manner, wherein at least anoccurrence of a defined reference event is followed by the counter valuein the counter memory unit is changed in at least one defined secondmanner, wherein at least in the course of a second defined communicationevent the first communication unit transmits the current counter valuein the counter memory unit directly or indirectly to the secondcommunication unit, wherein the first communication unit has at leastone first and a second data memory unit (MemA, MemB) and is configuredsuch that the occurrence of a defined trigger event is followed by acurrent data item in the first data memory unit (MemA) being written tothe second data memory unit (MemB) and by the counter value (MSG_CNT) inthe counter memory unit being changed in the defined second manner. 8.The communication system as claimed in claim 7, wherein the definedtrigger event is either a defined third communication event or aninternal trigger event.
 9. The communication system as claimed in claim7, wherein the first communication unit is configured such that, in thecourse of at least the second defined communication event between thefirst and second communication units, a current data item in the seconddata memory unit (MemB) is transmitted from the first communication unitto the second communication unit.
 10. A method for synchronizingcommunication between at least one first and a second communication unitin a communication system wherein the first communication unit has acounter memory unit which stores a counter value (MSG_CNT), wherein anoccurrence of a first defined communication event prompts the countervalue in the counter memory unit to be changed in at least one definedfirst manner and wherein an occurrence of a defined reference eventprompts the counter value in the counter memory unit to be changed in atleast one defined second manner, wherein, at least in the course of asecond defined communication event, the first communication unittransmits at least the current counter value (MSG_CNT) in the countermemory unit directly or indirectly to the second communication unit,wherein the first communication unit has at least one first and a seconddata memory unit (MemA, MemB), wherein the occurrence of a definedtrigger event is followed by a current data item in the first datamemory unit (MemA) being written to the second data memory unit (MemB)and by the counter value (MSG_CNT) in the counter memory unit beingchanged in the defined second manner and wherein an occurrence of thedefined second communication event is followed by a current data item inthe second data memory unit (MemB) being transmitted at least from thefirst communication unit to the second communication unit.
 11. Themethod as claimed in claim 10, wherein the defined trigger event iseither a defined third communication event or an internal trigger event.